1. Field of Invention
The invention relates to a damper unit positioned between an output shaft of an engine and a power transmission shaft of a power transmission system, and more particularly to an art for improving the method of installing the engine onto the power transmission shaft.
2. Description of Related Art
A combustion engine (hereinafter referred to as an engine), which is a prime mover of a vehicle, uses combustion pressure generated intermittently in a cylinder as drive force of the piston and then transmits it to the output shaft to obtain drive torque. Thus, torque vibration is generated in the output shaft. Conventionally, in a vehicle in which a manual transmission is disposed in a power transmission system, to damp the torque vibration and transmit it to the power transmission system, a fly wheel, which serves as inertial mass for damping an acceleration change component of the torque vibration, is installed on an engine output shaft, and a torsion damper, which is a displacement resistor for damping a velocity change component, is incorporated in a clutch. Also, in a vehicle in which an automatic transmission is disposed in a power transmission system, a torque converter is provided with vibration damping capacity, and thus a torsion damper is incorporated in a lock-up clutch for coupling an engine output shaft and a transmission mechanism.
Recently, a hybrid type vehicle provided with an engine and a motor (where a motor, a generator and an electric generator are hereinafter referred to as a motor) as its prime mover has been put into practical use. In such a vehicle, an engine output shaft, which vibrates due to its torque, is coupled to the motor, in which its torque vibration can be substantially reduced so that they can be driven together. Because the rotor shaft of the motor has a large inertial mass, when the torque of the engine and motor changes suddenly, an excessive torsion force to which the torsion damper cannot respond may be applied between the engine output shaft and the rotor shaft. Thus, a torque limiter is additionally provided to release such an excessive torsion force through slippage between both the shafts.
An example of such a damper unit with a torque limiter is disclosed in Japanese Patent Laid-Open Publication No. 10-267114 and is shown in FIG. 11. As shown in FIG. 11, in a torque limiter “a” of this damper unit, a friction plate “c” is provided on an outer periphery of a torsion damper “b” in which a damper spring is positioned between two discs, like a dry type single-plate clutch in a conventional manual transmission. The friction plate “c” is pressed onto the fly wheel “d” with a spring “e”. Thus, the torsion damper “b”, pressure plate “g”, spring “e”, and stopper ring “h” are installed in this order in the fly wheel “d”. Finally, they are mounted to the engine side by tightening the stopper ring “h” onto the fly wheel “d” with a bolt. Then, by coupling the power transmission shaft “i” of the power transmission system to the inner periphery of the torsion damper “b” by spline engagement, the engine and the power transmission system are assembled together. The power transmission system incorporates a motor that is assembled separately.
However, when installing the torsion damper “b” and parts “g”, “e”, and “h”, which form torque limiter “a”, onto the fly wheel “d” as described before, a fixing means for fixing the fly wheel “d” to a shaft end of the engine output shaft “f” is obstructed by the torsion damper “b”. This is because the torsion damper “b”, to which the power transmission shaft “i” is coupled through spline engagement, has a small inner peripheral diameter. Thus, the torsion damper “b” and the torque limiter “a” cannot be incorporated before the fly wheel “d” is installed onto the engine output shaft “f”.
Therefore, according to the conventional installation process, the torque limiter “a” needs to be installed onto the fly wheel “d” by tightening a bolt while aligning, for example centering, the axis of the torsion damper. Thus, some type of special tool for centering is necessary. In addition, when each component is installed in a vertical position to avoid a deflection of each component due to gravity, it is necessary to move the engine, which is both large and heavy, or to change the installation position of each component. Therefore, installation process inefficiencies are unavoidable.
Furthermore, the torque limiter “a” does not perform its function until a set load is applied on it when installed on the fly wheel “d” by tightening a bolt. Thus, in order to evaluate the performance of the torque limiter, it is necessary to also evaluate the engine and the fly wheel “d”. This leads to an inefficient component testing and evaluation process.